The present invention relates to an active matrix type display having a pixel electrode array which employs thin film transistors (TFT) as switching elements, and a method of manufacturing same.
The conventional active matrix type liquid crystal displays (AM-LCDs) have a liquid crystal element interposed between an array substrate and a counter substrate.
The array substrate includes a matrix array of pixel electrodes disposed on a transparent substrate such as a glass substrate, scanning lines disposed along the columns of the pixel electrode array, signal lines disposed along the electrode rows of the pixel electrode array, TFTs which control the pixel electrodes in response to the voltage signal applied to the scanning lines and the signal lines, and storage capacitor electrodes electrically connected to the pixel electrodes through an insulating layer.
The counter substrate includes a counter electrode disposed on a transparent substrate such as a glass substrate and confronted with the matrix array of the pixel electrodes, and a black matrix which shields the pixel electrodes. When the AM-LCD is used in a color display system, a color inking layer is disposed on the area surrounded by the black matrix and faces to the pixel electrodes.
The liquid crystal display supplies an "active" voltage to one of the scanning lines from the upper column of the matrix array and a "non-active" voltage to the other scanning lines. When each TFT is turned on through a switching interval, the TFT transmits the voltage applied on the signal line to the pixel electrode. And when each TFT is turned off through a holding interval, the voltage transmitted to the pixel electrode is held by the pixel capacitor composed between the pixel electrode and the counter electrode and the storage capacitor composed between the pixel electrode and the storage electrode.
The holding interval is equal to the interval of application of the active voltage. The transparency of the liquid crystal layer is changed according to the voltage between the pixel electrode and the counter electrode. The LCD displays the image by controlling the distribution of the transparency of the liquid crystal layer and modifying the light from a backlight source.
The aperture ratio of each pixel is indicated as a ratio of the transparent area to the whole pixel area. In the conventional LCDs, the aperture ratio is generally 30% to 40%. Accordingly, it is difficult to gain hopeful brightness. As a countermeasure to this problem, it is considered to increase the light intensity of the light source, but this measure has a shortcoming in that it results in the increase of power consumption.
It is considered to decrease the area of a driving circuit of each pixel as another measure, but it causes difficulty in maintaining production yield.